As nanotechnology pushes forward, the need increases for reliable methods of producing discrete nanostructures, either organic or inorganic, of specific shape and size, particularly in the 2-1000 nm regime. Two general approaches exist for making nanostructures: from the bottom up through chemical synthesis and from the top down through lithographic methodology. Techniques that target the region between the current capabilities of these two technologies, i.e., from about 2 nm to about 1000 nm, are currently highly sought after.
Prior art nanostructure synthesis methods that have been developed include focused-ion beam milling, scanning probe techniques, and x-ray lithography. While advanced mask-based lithography techniques are capable of producing large quantities of structures of small size, they are typically very expensive. Although milling techniques and scanning probe techniques are somewhat more affordable, they are primarily useful for the production of very small numbers of nanostructures. Further, all these available techniques are generally deployed to produce structures that are directly attached to surfaces or are integral parts of a surface. There are no general methods to produce mole quantity (6×1023) amounts of nanostructures that are lithographically defined. Such large quantities of nanostructures are almost by necessity solution based, since they would otherwise occupy a very large amount of surface area.
Biological systems utilize templated replication to produce large quantities of nanostructures such as nucleotide chains and peptide chains. Nucleotide synthesis is based upon hydrogen bond templating, followed by polymerization. Attempts have therefore been made to mimic the efficiency of oligonucleotide synthesis for various kinds of polymers, typically via hydrogen-bonded assembly or electrostatic assembly.
In general, polymerization of monolayers has been extensively studied. Many different routes to achieve non-patterned polymerization of a single monolayer have been investigated. Of particular relevance are polymerization systems that are topochemical in nature. A topochemical polymerization typically results in very little rearrangement of the monolayer once polymerization has occurred.
The poly(diacetylene)s (PDAs) exemplify such a system. PDA polymerization in both a self-assembled monolayer and in a Langmuir-Blodgett (LB) monolayer on gold has been achieved. FIG. 1 depicts a prior art scheme of diacetylene polymerization on a gold substrate by attachment of functionalized alkyl thiols. Attempts have been made to use hydrogen bonding to control polymerization in Langmuir-Blodgett monolayers. Since PDAs are polymerized by UV light, extensions to lithographic production of monolayers are relatively straightforward.
PDAs have also been polymerized in covalently bonded multilayers of monolayers. A multilayer film can be produced by covalent linkages, with the number of layers being controlled by a sequence of steps. Multilayer films have also been generated using hydrogen bonding and coordination bonding. FIG. 2 depicts a prior art approach to synthesis of a multilayer film, wherein a second monolayer is grown on a gold-alkyl thiol self-assembled monolayer (SAM) via hydrogen bonding (amide recognition).
Replication of siloxane monolayers through several generations on a substrate has also been reported. The monolayers replicate through what is understood to be an acetone-assisted process, involving hydrogen bonding and solvent intercalation for separating the replicate from the template. The replication process is not a one-pot process, nor are the monolayers specifically cross-linked or patterned. The monolayers are attached to the surface of a silicon substrate, and replication stalls after 4-5 generations. A method of replicating monolayers that is highly controlled and can be used to replicate patterns over many generations would be highly desirable and has never been reported.
Large scale two-dimensional polymers have often been produced by Langmuir-Blodgett techniques (Palacin et al., Thin Films 20:69-82 (1995)). One instance of patterned polymer multilayers that are free of a surface has been reported (Stroock et al., Langmuir 19(6): 2466-2472 (2003)), however, synthesis of two-dimensional lithographically defined single molecule polymers that can be readily suspended in a solvent has not.
Electroless plating of metals onto organic molecules is a common technique in biology, often used for histology staining. Electroless plating onto nanostructures has also been reported recently, using an amide template to coordinate metal ions as the electroless plating seeds (Matsui et al., J. Phys. Chem. B 104: 9576-79 (2000)). In addition, mineralization of organic structures is also a burgeoning field, and techniques for mineralizing CaCO3 and SiO2 are being developed and explored. Templating of semiconductor crystals has also been reported (Whaley S. R. et al., Nature 405: 665-668 (2000)).
Polymerization of nanoparticles has been reported in many ways. Typically, nanoparticles have been polymerized by using a polymerizable moiety in the ligand sphere of the nanoparticle (Boal et al., Adv. Functional Mat. 11(6): 461-465 (2001)), or by decorating a pre-existing polymer chain with nanoparticles (Walker et al., J. Amer. Chem. Soc. 123: 3846-3847 (2001)). Polymerization in films has been reported using dithiol chemistry (Musick et al., Chem. Mater. 12: 2869-2881 (2000)). Further, melting or agglomeration of nanoparticles into films is well known (U.S. Pat. No. 6,294,401, Ridley et al. (2001)). However, polymerization of a nanoparticle ensemble using a lithographically defined template has not been reported.
What has been needed, therefore, are techniques for making large quantities of nanostructures that target the region between the capabilities of current technology, i.e., from about 2 nm to about 1000 nm. In particular, what is needed is a method for synthesis of two-dimensional lithographically-defined single molecule polymers that can be readily suspended in a solvent, and may be further used to generate inorganic structures. What is further particularly needed is a method of replicating monolayers that is highly controlled and can be used to replicate patterns over many generations, preferably as a “one-pot” process producing monolayers that are specifically cross-linked or patterned.